System and method for measuring an amount of error associated with an optical amplifier

ABSTRACT

An optical signal having optical energy is received at an optical amplifier. The optical signal may be separated into a low frequency segment and a high frequency segment. The high frequency segment and the low frequency segment may be processed in order to determine a low frequency error signal and a high frequency error signal. The low frequency error signal may be summed with the high frequency error signal in order to generate a total error change associated with the optical amplifier.

RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No. 10/209,445, filed Jul. 30, 2002, now U.S. Pat. No.6,765,714 issued Jul. 20, 2004, which claims priority under 35 U.S.C.§119 to U.S. Provisional Application No. 60/308,940 filed Jul. 30, 2001.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of optical communicationsand more particularly to a system and method for measuring an amount oferror associated with an optical amplifier.

BACKGROUND OF THE INVENTION

Optical network architectures have grown increasingly complex in opticalcommunication systems. Optical communication systems may generally uselight waves as a medium for the transmission or the switching of data orinformation. Many optical communication systems may include an opticalamplifier that provides some gain to a corresponding system. Opticalamplifiers provide a valuable tool for optical communication systemsbecause of their ability to amplify, regenerate, or otherwise controloptical energy to be communicated to a next destination.

One drawback associated with some optical amplifiers is that they mayrequire precise design specifications in order to achieve a designatedgain. Optical amplifiers that are improperly designed, such that one ormore inaccuracies are produced in the propagation of data orinformation, may result in inadequate system performance. Often anoptical amplifier may be accompanied by one or more monitoring elementsthat ensure the amplifier input and output are within selected ranges.Optical amplifiers may also be designed to operate at high speeds withthe prescribed accuracy. High operational speeds generally result inquicker response times for an associated optical network. Providing anoptical amplifier that is highly accurate and stable, while maintaininghigh operational speeds, presents a significant challenge to designersand manufacturers associated with optical communication systems.

SUMMARY OF THE INVENTION

From the foregoing, it may be appreciated by those skilled in the artthat a need has arisen for an improved approach for monitoring one ormore parameters associated with an optical amplifier. In accordance withone embodiment of the present invention, a system and method formeasuring an amount of error associated with an optical amplifier areprovided that substantially eliminate or greatly reduce disadvantagesand problems associated with conventional amplifier managementtechniques.

According to one embodiment of the present invention, there is provideda method for measuring an amount of error associated with an opticalamplifier that includes receiving an optical signal, that comprisesoptical energy. The optical signal may be separated into a low frequencysegment and a high frequency segment. The high frequency segment and thelow frequency segment may be processed in order to determine a lowfrequency error signal and a high frequency error signal. The lowfrequency error signal may be summed with the high frequency errorsignal in order to generate a total error change associated with theoptical amplifier.

Certain embodiments of the present invention may provide a number oftechnical advantages. For example, according to one embodiment of thepresent invention, an approach for measuring an error associated with anoptical amplifier is provided that offers the ability to adjust a 31 (orgreater) channel transient. As a result of the detected error, the gainassociated with the optical amplifier may be maintained or otherwisecontrolled by managing power levels provided to the optical amplifier.This management may be executed dynamically at a level 0.05 dBm orgreater within the designated optical amplifier gain.

Another technical advantage associated with one embodiment of thepresent invention is a result of the preciseness in measuring an errorassociated with an optical amplifier input, output, or gain. Theprecision in making the measurement determination allows for increasedstability of a corresponding optical amplifier, whereby the long-termgain associated with the optical amplifier is maintained at stablelevels as a result of the splitting of the control into a high frequencysegment and low frequency segment. The low frequency segment mayintegrate one or more low frequency components of the signal and thusforce a long-term error to a result of zero.

Yet another technical advantage associated with one embodiment of thepresent invention relates to the separation of an optical signal intolow frequency and high frequency components. This separation resultsfrom the recognition that one or more electronic components within acorresponding optical communication have varying intrinsic qualities.For example, a component or segment associated with a low frequencyrange may maintain a suitable low offset value (e.g., lower directcurrent errors due to temperature) but not necessarily maintain good oradequate high frequency characteristics. Conversely, high frequencysegments generally may not maintain suitable direct currentcharacteristics. Accordingly, a separation of the high and low frequencycomponents may be used in order to address these limitations and providefor increased accuracy in determining an error associated with theoptical amplifier. The separation of the incoming signal into lowfrequency and high frequency components may further simplify overalloperations associated with a corresponding optical communication systemwhile maintaining faster processing times. Embodiments of the presentinvention may enjoy some, all, or none of these advantages. Othertechnical advantages may be readily apparent to one skilled in the artfrom the following figures, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present invention andfeatures and advantages thereof, reference is made to the followingdescription, taken in conjunction with the accompanying figures, whereinlike reference numerals represent like parts, in which:

FIG. 1 is a simplified block diagram of an optical communication systemfor measuring an amount of error associated with an optical amplifier;

FIG. 2A is a simplified block diagram of an input power monitor elementincluded within the optical communication system;

FIG. 2B is a schematic diagram of an example implementation of the inputpower monitor element of FIG. 2A;

FIG. 3A is a simplified block diagram of an output power monitor elementincluded within the optical communication system;

FIG. 3B is a schematic diagram of an example implementation of theoutput power monitor element of FIG. 3A; and

FIG. 4 is a flowchart illustrating a series of example steps associatedwith a method for measuring an amount of error associated with anoptical amplifier.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 a simplified block diagram of an optical communication system 10for measuring an amount of error associated with an optical amplifier 12in accordance with one embodiment of the present invention. FIG. 1provides an overview of an example arrangement of optical communicationsystem 10 and where appropriate may be designed or constructed usingvarious other configurations in accordance with particular needs.Optical communication system 10 may include optical amplifier 12, anautomatic gain control 16, an input power monitor element 18, and anoutput power monitor element 22. Input power monitor element 18 andoutput power monitor element 22 may be positioned on a single integratedcircuit chip (or multiple integrated circuit chips where appropriate) oralternatively included within a module that may include opticalamplifier 12.

Optical communication system 10 may be positioned at any suitablelocation within or external to an optical network in order to facilitatethe delivery, transmission, or switching of optical information or datain an optical communications environment. Where appropriate, opticalcommunication system 10 may be included in a pre-amp segment of anoptical network or architecture. An arbitrary input signal may beprovided to optical amplifier 12 and selected based on one or moreproperties associated with a corresponding communications architecture.Alternatively, the input signal may be designated based on one or moreparameters associated with any of the elements included within opticalcommunication system 10.

In accordance with the teachings of the present invention, opticalcommunication system 10 operates to provide an element that measures anamount of error associated with optical amplifier 12. In response to theerror detection, the gain associated with optical amplifier 12 may bedynamically corrected or otherwise managed at an accuracy that producesa resultant gain substantially similar to the targeted desired gain. Inorder to achieve significant error detection accuracy, an incomingoptical signal may be divided into separate frequency components. Thereason for this separation may be due to characteristics of one or moreelectronic components included within an optical communicationsarchitecture. For example, low frequency segments may maintainbeneficial low offset values (e.g. low direct current (DC) errors due totemperature) but may not necessarily possess beneficial high frequencycharacteristics. Conversely, high frequency segments may not haveadequate DC characteristics. Accordingly, the separation of high and lowfrequency components from an optical signal may address one or moreissues associated with the limitations of optical components includedwithin an optical communications architecture.

The result of this separation is a configuration that achieves enhancedprocessing speeds such that a 31-channel transient (or less or greaterin accordance with particular communication properties) may be properlyadjusted. Optical communication system 10 may operate at a processingspeed in the approximate range of 3e⁻⁶ seconds per cycle (or faster)that may ensure that power levels associated with optical amplifier 12are maintained at a consistent level. Additionally, such an architecturemay keep a long-term gain associated with optical amplifier 12 stabledue to the splitting of the controls into a high frequency segment and alow frequency segment. The low frequency segment may integrate lowfrequency components of the signal and the high frequency segmentintegrates high frequency components of the signal. This division mayenable the long term error associated with optical amplifier 12 to reacha zero value and thereby enhance the efficiency of opticalcommunications.

Optical amplifier 12 is an element that receives optical energy and thatmay use a feedback control loop in order to generate a power outputsignal. Optical amplifier 12 may detect, regenerate, amplify, orotherwise modify an incoming power signal in order to produce a selectedoutput. Optical amplifier 12 may include one or more correspondinginputs that provide optical energy or adequate feedback to opticalamplifier 12. The optical power being directed to optical amplifier 12may be monitored by input power monitor element 18. Any suitablecommunicative interface may be provided between optical amplifier 12 andinput power monitor element 18. In addition, the optical output ofoptical amplifier 12 may be monitored or otherwise evaluated by outputpower monitor element 22. Accordingly, a suitable interface may beprovided between output power monitor element 22 and optical amplifier12 that establishes a suitable communication link.

Optical amplifier 12 may also be referred to as a ‘repeater’ and may becapable of reproducing an optical signal or any portion thereofgenerated at any location within an associated optical network. Inaccordance with one embodiment of the present invention, opticalamplifier 12 is an erbium doped fiber amplifier (EDFA). Alternatively,optical amplifier 12 may be any other suitable amplifier, potentiallyinclusive of a semiconductor material and suitably doped with any otherappropriate element in order to properly amplify, manipulate, reproduce,or process an input signal for communication to a suitable nextdestination. The erbium element within optical amplifier 12 may includestate transitions that cause the emission of photons concurrently withthe reception of an incoming signal.

The input to optical amplifier 12 may be supplied by one or more pumplasers where appropriate. Alternatively, any other suitable element mayprovide an adequate input signal to optical amplifier 12. Opticalamplifier 12 may make appropriate adjustments to the power providedthereto by cooperating with automatic gain control 16 when a change isexperienced in input power. These adjustments to a power input value maybe further effectuated with a suitable feedback control loop,potentially inclusive of automatic gain control 16. Such an operationmay bring the power output of optical amplifier 12 back to its targetedvalue and compensate for the change in input power provided to opticalamplifier 12.

The changes in input power experienced by optical amplifier 12 mayresult from an upstream fault of some type within the optical networkassociated with optical amplifier 12. Optical amplifier 12 or automaticgain control 16 may signal when an error or a failure has occurred suchthat a suitable input power level may be subsequently supplied tooptical amplifier 12.

Automatic gain control 16 is a feedback element operable to receive oneor more signals associated with optical amplifier 12 and to providefeedback data such that one or more parameters may be recorded,modified, or otherwise changed in order to generate a predetermined gainassociated with optical amplifier 12. There are generally twofundamental gain classes, one that may be used for a physicalcalibration of an individual optical element or component and one thatis representative of the gain of a portion of an optical systemarchitecture associated with a system input and output. The system gainmay reflect the optical gain of optical amplifier 12. This gain may bereflected by a ratio of the input signal and the output signal. This maybe accomplished by subtracting out the output signal value after it hasbeen scaled down by a multiplying digital to analog converter andfurther subtracting out the system offset that is representing anamplified stimulated emission (ASE) noise from the input low frequencysignal. The result produced may be representative of an integral of alow frequency error signal as described below.

Automatic gain control 16 may compute the instantaneous gain of opticalamplifier 12 by using information supplied by input power monitorelement 18 or output power monitor element 22. The gain that is computedmay be compared with a target or a predetermined gain that is suppliedto automatic gain control 16 by any suitable element. Differencesbetween the computed instantaneous gain of optical amplifier 12 and thetarget gain may be eliminated or otherwise reduced by automatic gaincontrol 16 through adjustment of one or more currents supplied to acorresponding pump laser that feeds optical amplifier 12.

In operation of an example embodiment, optical amplifier 12 may receivea power input and suitably amplify or reproduce the power input suchthat a predetermined or selected power output is provided. A fraction ofthe power input may be directed to input power monitor element 18 suchthat input power monitor element 18 may divide or otherwise evaluate thepower being provided to optical amplifier 12. Alternatively, this inputpower may be monitored by a coupler or any other suitable deviceoperable to receive a power input signal provided to optical amplifier12. Input power monitor element 18 may then properly separate lowfrequency and high frequency components from the incoming opticalsignal. This may enhance the speed of one or more processing cycles suchthat information or data may be more quickly processed in opticalcommunication system 10. Additional details relating to frequencydivision operations and phase/amplitude manipulations are provided belowwith reference to specific circuitry included in each of input powermonitor element 18 and output power monitor element 22.

Input power monitor element 18 is an element that includes one or morecomponents operable to separate an incoming optical signal provided tooptical amplifier 12 into low frequency and high frequency segments.Input power monitor element 18 includes example circuitry that comprisesvarious electronic components and elements operable to achieve thisseparation. It is important to note that, where appropriate, these partsmay be substituted with other electronic parts arranged in various otherconfigurations in order to achieve a separation of an optical signalinto various frequency segments. The embodiments illustrated in FIGS. 2Aand 2B have only been offered for purposes of example as numerous otherelectronic architectures may be employed in accordance with particularneeds without departing from the teachings of the invention.

Output power monitor element 22 is an element that includes one or morecomponents operable to assist in separating an incoming optical signalinto multiple frequency components. Additionally, output power monitorelement 22 may be coupled to an output associated with optical amplifier12 such that an output power level may be identified or otherwisemonitored. Output power monitor element 22 has been illustrated asinclusive of one or more electronic components that provide a monitoringfunction for the output power provided by optical amplifier 12 and thatmay assist in the division of an optical signal into high frequency andlow frequency segments. Where appropriate, these elements and componentsmay be substituted with other electronic parts arranged in various otherappropriate configurations. Additionally, numerous other electronicarchitectures may be employed in accordance with particular needswithout departing from the teachings of the invention. The circuitryprovided within output power monitor element 22 has only been offeredfor purposes of example and should not be construed to limit variousother potential implementations of output power monitor element 22.

Input power monitor element 18 and output power monitor element 22 maycooperate in order to provide an enhanced control function that affectsoptical amplifier 12. This is a result of the separation of an opticalsignal into high frequency and low frequency segments. This may achievean accurate, stable, and fast pre-amplifying control system that makesan architecture less likely to lose optical communications traffic. Suchan approach may be implemented in order to design a control system thatoperates at speeds of three microseconds or less in order to adjust to a32 to 1 channel transient in one embodiment. Optical communicationsystem 10 may operate to keep power levels at an optimal level byadjusting the gain of optical amplifier 12 dynamically to 0.05 dBm ofthe selected gain. In addition, the long-term gain associated withoptical amplifier 12 may be kept stable as a result of the splitting ofthe amplifier control into a high frequency faction and a low frequencyfaction.

The implementation of input power monitor element 18 and output powermonitor element 22 may also enhance the accuracy in controllingparameters associated with optical amplifier 12. Accuracy is improved bydividing input (and potentially output signals) into separate frequencycomponents. This separation may in turn be beneficial, in part, becauselow frequency electronic components generally have a specific set ofdesirable characteristics, such as low offset and low DC errors, thatmay result from temperature changes in a corresponding system. Thesecharacteristics may not necessarily be found in high frequencyelectronic components. In addition, low frequency electronic componentsgenerally do not have certain characteristics often found in highfrequency electronic components, such as for example an associated gainat a frequency level of 500 MegaHertz (MHz). Thus, the separation ofoptical signals within a control system into high and low frequencysegments may be effectuated by optical communication system 10 in orderto enhance the efficiency and processing capabilities thereof byprecisely monitoring one or more parameters associated with opticalamplifier 12 such that an error or a change may be identified.

FIG. 2A is a simplified block diagram of input power monitor element 18included within optical communication system 10. Additionally, FIG. 2Bis an example schematic diagram of one implementation of input powermonitor element 18. FIG. 2B also provides details relating to examplecircuitry that may be included within input power monitor element 18.The elements included within input power monitor element 18 may beprovided using hardware, software, or any other suitable component,element, or object in accordance with particular needs.

Input power monitor element 18 may include one or more current mirrors28 and 30 that facilitate the separation of an optical signal intofrequency segments. Input power monitor element 18 may also include anoptical to electronic pin diode converter 34. Input power monitorelement 18 may also include multiple amplifiers 38, 40, 42, and 44 thatmay be any suitable type of amplifier (e.g. operational amplifier,transimpedance amplifier, etc.) in accordance with particular needs.Input power monitor element 18 may also include a set of digitallycontrolled resistors 50 and 52.

The elements included within input power monitor element 18 may becoupled to each other in any suitable fashion using any number ofvarious suitable electronic components such as wires, resistors,inductors, capacitors, and any other suitable electronic elements,components, hardware, or software that are operable to facilitate thecommunication between one or more of these elements. In addition, theseelements may cooperate in order to suitably process or otherwise monitoran input power provided to optical amplifier 12. The input power maythen be properly separated into high frequency and low frequencysegments such that processing speeds may be increased and a suitablegain may be accurately reflected by optical amplifier 12.

In operation, diode converter 34 may measure the input power to opticalamplifier 12. The high frequency component of the input power measuredby diode converter 34 may be processed through amplifiers 38 and 40. Thelow frequency component of the input power measured by diode converter34 may be processed through current mirrors 28 and 30. Current mirrors28 and 30 may be any suitable current mirror element, such as a Wilsoncurrent mirror for example, that maintains a constant voltage across oneor more segments of diode converter 34.

Amplifier 38 may be a fixed gain transimpedance amplifier in accordancewith one embodiment of the present invention. Alternatively, amplifier38 may be any other suitable type of amplifier operable to receive orotherwise process information provided by diode converter 34. Amplifier40 may be a digitally controlled, variable gain, high frequencyamplifier. This arrangement creates a variable gain stage that may beused to correct the optical tap coupling variations and the particularresponsivity of diode converter 34. Alternatively, amplifier 40 may beany other type of amplifier operable to receive and process opticalinformation or data provided by diode converter 34. The output of thevariable gain stage may be coupled in an alternating current (AC)fashion to another amplifier that may buffer the processed signal in thehigh frequency section of the control system.

As identified above, there are generally two fundamental gain classes,one that may be used for system physical calibration and one that isrepresentative of the entire gain of the system. The calibration gainsare identified above in connection with the variable gain stage formedby amplifiers 38 and 40. The system gain reflects the optical gain ofoptical amplifier 12. This gain may be reflected by a ratio of the inputsignal and the output signal.

Current mirrors 28 and 30 are electronic configurations that comprisevarious electronic elements operable to maintain a constant voltageacross diode converter 34. By maintaining a constant voltage acrossdiode converter 34, a constant capacitance associated diode converter 34may also be maintained. In addition, the voltage across diode converter34 may be kept constant, for example as close as five volts as possible,in order to maintain the smallest capacitance reasonably possible.Current mirrors 28 and 30 may provide this function while allowing oneor more operational amplifiers, such as amplifier 42 for example, to beused in a transimpedance configuration, so that current is beingsystematically converted into a suitable voltage.

Current mirror 28 may feed amplifier 42. Amplifier 42 and gaincontrolling digitally controlled resistor 52 may together collectivelyform a variable gain stage. The variable gain stage may be used tocorrect for the optical tap coupling variations in addition to theresponsivity of diode converter 34. The output of this stage may becommunicated to a next suitable amplifier that buffers the low frequencysumming point for the proportional plus integration (PPI) section ofoptical communication system 10.

Current mirror 30 may feed amplifier 44. Amplifier 44 and gaincontrolling digitally controlled resistor 50 may together collectivelyform a variable gain stage. This variable gain stage may be used tocorrect for the optical tap coupling variations plus the responsivity ofdiode converter 34. The output of this stage may be communicated to asuitable amplifying element (and/or its associated circuitry) that maybuffer the signal as part of a feed forward portion of a controlledsystem. In addition, this information may be communicated to the lowfrequency summing point for the PPI section of the architecture. Theoutput of this stage may be fed into a low frequency amplifierpositioned in any suitable element, such as a recovery controller forexample, that may be used for loss of signal detection.

Because of the sensitive nature of the operations described thateffectuate the division of an incoming signal into high frequencysegments and low frequency segments, one or more of the materialsincluded within optical communication system 10 may be specificallyselected for their intrinsic characteristics. For example, opticalcommunication system 10 may be suitably mounted on a printed circuitboard material for use in connection with additional amplifyingelements, where appropriate, that may include a significantly highersurface and bulk resistivity (such as Rogers 4350 printed circuit boardstock material for example). The matching of printed circuit boardmaterial may provide an insulating benefit given the low signal levelsbeing detected by a corresponding loss of signal detector. In addition,all of the elements described as within input power monitor element 18and output power monitor element 22 may include guard traces in order todeter stray currents from interfering with one or more signal currentspresented in these regions.

FIG. 3A is a simplified block diagram of output power monitor element 22included within optical communication system 10. Additionally, FIG. 3Bis an example schematic diagram of one implementation of output powermonitor element 22. FIG. 3B also provides details relating to examplecircuitry that may be included within output power monitor element 22.The elements included within output power monitor element 22 may beprovided using hardware, software, or any other suitable component,element, or object in accordance with particular needs.

Output power monitor element 22 may include multiple amplifiers 60, 62,and 64. In addition, output power monitor element 22 may include acurrent sensing resistor 70 and a digitally controlled resistor 72.Output power monitor element 22 may also include an optical toelectronic pin diode converter 76. Where appropriate, these elements maybe modified considerably or substituted appropriately in accordance withparticular needs of a corresponding system. Additionally, numerous othercomponents may be included within output power monitor element 22without departing from its operation or its teachings as describedherein.

Diode converter 76 may measure the output power from optical amplifier12. The high frequency component of the output power measured by diodeconverter 76 may be processed through amplifier 64. Amplifier 64 may bea transimpedance amplifier in accordance with one embodiment of thepresent invention. However, amplifier 64 may alternatively be any othersuitable amplifier where appropriate and in accordance with particularneeds. The output power measured by diode converter 76 may be bufferedby amplifier 62 after it is received from amplifier 64. The gain controlof this signal may be provided to and further managed via a nextsuitable amplifier.

The low frequency component of the output power measured by diodeconverter 76 may be processed by current sensing resistor 70. Currentsensing resistor 70 may develop a voltage proportional to the currentpassing through diode converter 76. In addition, the voltage acrosscurrent sensing resistor 70 may be sensed with amplifier 60. Amplifier60 may be an instrumentation amplifier in accordance with one embodimentof the present invention. However, amplifier 60 may also be any othersuitable type of amplifier where appropriate. The gain of amplifier 60may be controlled by digitally controlled resistor 72.

The summation and integration of the low frequency input signal, the lowfrequency output signal, and the offset may be executed at any suitableamplifier. This may be effectuated in a low frequency domain due, inpart, to the fact that an integrator should be a low temperaturecoefficient device. Simultaneously, the high frequency input and outputsignals may be summed using a high frequency operational amplifier.

High frequency scaling may be accomplished by one or more amplifiersthat are controlled by a digitally controlled voltage source. The scaledhigh frequency output may be subtracted from the high frequency input inorder to provide a high frequency error signal. This error signal maythen be used by optical communication system 10 in order to manage orotherwise control a gain associated with optical amplifier 12.

The low and high frequency error signals may be added together afterthey are properly filtered. The low frequency signal may be passedthrough a low pass filter and the high frequency signal is passedthrough a high pass filter. The corners of these filters may overlapsuch that an enhancement of the middle frequencies is executed. Anamplifier that is summing these signals may add a lead networkcharacteristic in order to compensate for the lag in the pumplaser—optical amplifier 12 combination. Any other additional suitableoffsetting value may be added where appropriate and according toparticular needs. A final lag may also be added that allows for thecontrol system to pass through a unity gain before the pure delay of theoptical fiber associated with the architecture adds too much of a phaseshift to the control loop.

The result of this frequency, amplitude, and phase manipulation for theabove-described embodiment may be a system that (for example) can trackerror changes in an optical system to approximately 0.05 dB from a 32 to1 channel transient. This may result in the precise identification of anerror associated with optical amplifier 12. This identification may thenresult in the ability to control the gain associated with opticalamplifier 12. In addition, such an arrangement may provide for thestable management of power provided to optical communication system 10.This error detection configuration is generally not susceptible to losttraffic or inadequate system speed.

FIG. 4 is a flowchart illustrating a series of example steps associatedwith a method for measuring an amount of error associated with opticalamplifier 12. The method begins at step 100 where an optical signal maybe communicated to optical amplifier 12. At step 102, opticalcommunication system 10 may invoke input power monitor element 18 andoutput power monitor element 22 such that the incoming optical signalmay be suitably separated into a high frequency component and a lowfrequency component. At step 104, the high frequency component and thelow frequency component may be suitably processed and summed in order togenerate one or more low frequency error signals and one or more highfrequency error signals.

At step 106, the low frequency error signals and the high frequencyerror signals may be properly summed in order to generate a total errorchange. The total error change represents the frequency, amplitude, andphase manipulation executed by optical communication system 10. Opticalcommunication system 10 may be capable of accurately tracking errorchanges associated with a corresponding optical amplifier 12. The errorchange value may precisely identify an error associated with opticalamplifier 12. At step 108, this error change value may then be utilizedin effectuating control or otherwise influencing the gain associatedwith optical amplifier 12 or any other amplifying parameter whereappropriate and according to particular needs.

Although the present invention has been described in detail withreference to particular embodiments, it should be understood thatvarious other changes, substitutions, and alterations may be made heretowithout departing from the spirit and scope of the present invention.For example, although the present invention has been described withreference to a number of potentially suitable amplifiers, any suitabletype of amplifier may be used in the amplifier applications oroperations described above. The error detection methods as describedabove in conjunction with optical communication system 10 mayadditionally include other applications for feedback loops or opticalamplification systems that rely on accurate error determinations forconsistent operation or functionality.

In addition, although FIG. 1 illustrates an arrangement of selectedelements, numerous other components may be used in combination withthese elements without departing from the teachings of the presentinvention. For example, elements such as optical switches, opticalmultiplexers, filters, diffraction gratings, couplers, splitters, andnumerous other suitable components may be included or coupled to opticalcommunication system 10. The embodiment illustrated in FIG. 1 has onlybeen offered for purposes of teaching and where appropriate may beinclusive of various other suitable components that facilitate theidentification of an error associated with a target optical amplifier.

Moreover, although FIGS. 2A–3B have been described with reference tospecific electronic elements in various configurations, any suitablearchitecture may be provided in conjunction with optical communicationsystem 10 without departing from the scope of the present invention.Other appropriate optical architecture components or suitable elementssuch as resistors, inductors, capacitors, and amplifiers may be includedwithin the illustrated embodiment in any appropriate arrangement. Thesealternative designs may be provided, designated, or otherwise selectedin order to offer specific operational parameters that may in turninfluence one or more optical communication operations.

Additionally, although optical communication system 10 describes anappropriate separation of an optical signal into high frequency and lowfrequency segments, any suitable frequency division may be made. Thismay be inclusive of multiple frequency divisions that provide a moreaccurate basis from which to monitor one or more parameters associatedwith optical amplifier 12.

Numerous other changes, substitutions, variations, alterations, andmodifications may be ascertained by those skilled in the art and it isintended that the present invention encompass all such changes,substitutions, variations, alterations, and modifications as fallingwithin the spirit and scope of the appended claims. Moreover, thepresent invention is not intended to be limited in any way by anystatement in the specification that is not otherwise reflected in theappended claims.

1. An apparatus for measuring an amount of error associated with anoptical amplifier, comprising: an optical amplifier, the opticalamplifier being associated with an optical signal; a power monitorelement coupled to the optical amplifier, the power monitor elementoperable to receive at least a portion of the optical signal associatedwith the optical amplifier, the power monitor element operable toidentify at least one of a low frequency segment and a high frequencysegment of the optical signal; an automatic gain control elementoperable to receive the at least one of the low frequency segment andthe high frequency segment of the optical signal identified by the powermonitor element, the automatic gain control element operable to controla gain of the optical amplifier in response to either or both of the lowfrequency segment and the high frequency segment of the optical signal.2. The apparatus of claim 1, wherein the optical signal associated withthe optical amplifier is an input optical signal received by the opticalamplifier.
 3. The apparatus of claim 1, wherein the optical signalassociated with the optical amplifier is an output optical signalgenerated by the optical amplifier.
 4. An apparatus for measuring anamount of error associated with an optical amplifier, comprising: anoptical amplifier, the optical amplifier being associated with anoptical signal; a power monitor element coupled to the opticalamplifier, the power monitor element operable to receive at least aportion of the optical signal associated with the optical amplifier, thepower monitor element operable to identify at least one of a lowfrequency segment and a high frequency segment of the optical signal; anautomatic gain control element operable to receive the at least one ofthe low frequency segment and the high frequency segment of the opticalsignal identified by the power monitor element, the automatic gaincontrol element operable to control a gain of the optical amplifier inresponse to the at least one of the low frequency segment and the highfrequency segment of the optical signal; wherein the power monitorelement is operable to generate at least one of a low frequency segmentand a high frequency segment associated with an input optical signal tothe optical amplifier and an output optical signal from the opticalamplifier.
 5. The apparatus of claim 4, wherein the automatic gaincontrol element is operable to generate at least one of a low frequencyerror signal from the low frequency segments associated with the inputoptical signal and the output optical signal and a high frequency errorsignal from the high frequency segments of the input optical signal andthe output optical signal.
 6. The apparatus of claim 5, wherein theautomatic gain control element is operable to determine a total errorchange in response to the at least one of the low frequency error signaland the high frequency error signal.
 7. The apparatus of claim 6,wherein the total error change is utilized to control the gain of theoptical amplifier.
 8. The apparatus of claim 1, wherein the powermonitor element is operable to identify one or more intermediatefrequency segments.
 9. The apparatus of claim 8, wherein the automaticgain control element is operable to control a gain of the opticalamplifier in response to the low frequency segment, the high frequencysegment, and the one or more intermediate frequency segments of theoptical signal.
 10. The apparatus of claim 1, wherein the automatic gaincontrol element is operable to compare the gain of the optical amplifierto a target gain associated with the optical amplifier.
 11. A method formeasuring an amount of error associated with an optical amplifier,comprising: receiving at least a portion of an optical signal associatedwith an optical amplifier; identifying at least one of a low frequencysegment and a high frequency segment of the optical signal; controllinga gain of the optical amplifier in response to either or both of the lowfrequency segment and the high frequency segment of the optical signal.12. A method for measuring an amount of error associated with an opticalamplifier, comprising: receiving at least a portion of an optical signalassociated with an optical amplifier; identifying at least one of a lowfrequency segment and a high frequency segment of the optical signal;controlling a gain of the optical amplifier in response to the at leastone of the low frequency segment and the high frequency segment of theoptical signal; generating the low frequency segment for an inputoptical signal to the optical amplifier and an output optical signalfrom the optical amplifier; generating a low frequency error signal fromthe low frequency segments associated with the input optical signal andthe output optical signal.
 13. The method of claim 12, furthercomprising: generating the high frequency segment for an input opticalsignal to the optical amplifier and an output optical signal from theoptical amplifier; generating a high frequency error signal from thehigh frequency segments of the input optical signal and the outputoptical signal.
 14. The method of claim 13, further comprising:combining the low frequency error signal and the high frequency err orsignal into a total error change associated with the optical amplifier.15. The method of claim 14, further comprising: adjusting the gain ofthe optical amplifier in accordance with the total error change.
 16. Asystem for measuring an amount of error associated with an opticalamplifier, comprising: means for receiving at least a portion of anoptical signal associated with an optical amplifier; means foridentifying at least one of a low frequency segment and a high frequencysegment of the optical signal; means for controlling a gain of theoptical amplifier in response to either or both of the low frequencysegment and the high frequency segment of the optical signal.
 17. Asystem for measuring an amount of error associated with an opticalamplifier, comprising: means for receiving at least a portion of anoptical signal associated with an optical amplifier; means foridentifying at least one of a low frequency segment and a high frequencysegment of the optical signal; means for controlling a gain of theoptical amplifier in response to the at least one of the low frequencysegment and the high frequency segment of the optical signal; means forgenerating the low frequency segment for an input optical signal to theoptical amplifier and an output optical signal from the opticalamplifier; means for generating a low frequency error signal from thelow frequency segments associated with the input optical signal and theoutput optical signal.
 18. The system of claim 17, further comprising:means for generating the high frequency segment for the input opticalsignal to the optical amplifier and the output optical signal from theoptical amplifier; means for generating a high frequency error signalfrom the high frequency segments of the input optical signal and theoutput optical signal.
 19. The system of claim 18, further comprising:means for combining the low frequency error signal and the highfrequency error signal into a total error change associated with theoptical amplifier.
 20. The system of claim 19, further comprising: meansfor adjusting the gain of the optical amplifier in accordance with thetotal error change.